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Hardness reference blocks are used for annual verification and calibration of hardness testing machines, the periodic (daily) check (see page 7) and sometimes for overtaking of hardness scales on a hardness testing machine. That's why they are a necessary help of industrial Quality Management. Only the use of high quality, precise hardness reference blocks calibrated to applicable standards can ensure the functionality and relative reliability and accuracy of
measurement of a hardness testing machine.
The quality requirements for hardness reference blocks in
respect of the necessary homogeneity, microstructure stability,
uniformity of hardness, surface quality, are described in the corresponding
international, european and national standards, and are
easily exceeded by the Buderus blocks. The limits for the single
parameters were much reduced within the internal guideline
agreed upon with the materials testing institute of Nordrhein-
Westfalen (MPA NRW). For the mechanical treatment for instance
the parameters for roughness, flatness, and parallelism are
reduced to half the values of the standards. This requires extremely
sophisticated production, starting with the selection and production
of suitable input stock, and including complicated heat
treatment processes, extremely careful machining and calibration
at the MPA NRW.
The hardness reference blocks used for indirect verification
should conform largely to the work piece to be tested, in terms of
material characteristics and hardness range.For this reason a hardness
reference block made of aluminium was developed for the
lower hardness range which can not be covered by steel, using
new materials technology methods.
The division of MPA NRW responsible for calibration of
hardness reference blocks has been accreditated as DKDcalibration
Laboratory of Deutscher Kalibrierdienst (DKD) by
the Physikalisch Technische Bundesanstalt (PTB), signatory of
the multilateral agreement of the European Cooperation for
Accreditation (EA) for mutual recognition of calibration certifcates.
That ist one of the reasons why the calibrated hardness
reference blocks distributed by Buderus are accepted without
reservation not only in Germany but as well internationally.
When using hardness reference blocks it is irrelevant whether
the value of the nominal hardness to be delivered corresponds
exactly to the actual calibration
value observed, since scale
adaptation should be carried
out with at least two hardness
values.
A hardness reference block
shall only be used as according
to the standards to that method
and test condition for which it
was calibrated.
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Rockwell |
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Hardness Reference Blocks made
of Steel for the Rockwell Test |
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The method most commonly used for hardness testing of metal
materials is the Rockwell hardness test,because of it's simplicity of
operation and evaluation,and capability for automation. The hardness
value is determined by measuring the permanent depth of
indentation. The various hardness scales differ in terms of
. indenter
. preliminary test force
. total test force
. calculation of the hardness value.
Depending on the particular test condition, the indenter used
is a diamond cone or a hard metal alloy ball (W) or a steel ball (S).
Buderus Rockwell test blocks with a test certificate from
MPA NRW are available for all standard test methods. |
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| According to the new Rockwell standard the use of a square
block with a larger thickness however is highly recommended. |
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Hardness Reference Blocks made
of Steel for the Vickers Test |
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Vickers hardness test is comparable to that of Brinell, but
the indenter used is a diamond pyramid with a square base. The
hardness value is calculated using the test force and the length of
the centre diagonal of the resultant impression.
Depending on the test force, a distinction is made in the Vickers
test plates available between
. Micro blocks (HV 0.005 to HV 10)
. Macro blocks (HV 1 to HV 150) |
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Hardness Reference Blocks made
of Steel for the Knoop Test |
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| The Knoop hardness test is similar to that of Vickers. The
indenter used is a diamond pyramid with rhombic base. |
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Brinell |
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Hardness Reference Blocks made
of Steel for the Brinell Test |
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In the Brinell test an indenter (ball) is pressed into the surface
of a sample, and the resultant diameter of the indentation is measured.
Since 1999 only hardmetal alloy balls (HBW) are used as
indenters.
Buderus Brinell test blocks are produced in different sizes
and different surface finishes depending on the ball diameter. |
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Hardness Reference Blocks made
of Aluminium |
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For several years there has been a need for "soft"blocks. Using
new materials technology methods, it is now possible to produce
hardness reference blocks made of aluminium. They are available
in the nominal hardness values 60 HV30,80 HV30 and 100 HV 30
in two different block sizes depending on the test. |
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Hardness Reference Blocks made of
Steel for the Martens Hardness Test |
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The hardness testing method Martens HM (till now Universal
hardness HU) is a registrating method,which incorporates the possibility
for the determination of further materials parameters
according to existing standards. The test is carried out force or
indentation depth controlled with an indenter, which is in most
cases a diamond according to Vickers. The method is especially
used for thin hard layers and coatings. |
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Quality Insurances
for Hardness Testing |
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For the quality insurance the standards published since 1999
recommend, as addition to annual calibration and verification, a
daily check of the hardness testing machines. For documentation,
calculation and presentation of the quality insurance for all hardness
reference blocks distributed by Buderus an EXCEL-program
has been created, in which e.g. the calibration values, the allowed
values for the error and the repeatability of the hardness testing
machine and the uncertainty of the reference block are integrated.
This program and further information may be overtaken by download
from URL: http://www.mpanrw.de/crm.When inserting the
MPA NRW number and the hardness value of the reference block,
the download can be started by a click on OK. When inserting
"demo"on both positions a test version of one block as an example
is downloaded. When using a hardness reference block together
with the program for hardness testing machines the uncertainty of
measurement and - according to the standard - the repeatability
and the error are determined (Bibliographical References p. 8). In
the program is controlled and displayed as text whether the values
of the machine are according to the standard or not.
For the determination of uncertainty the program offers two
possibilities
- one without the correction of the error according to UNCERT
proposal of SMT of EU and
- one including the correction of error from nominal value. |
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Standards and Bibliographical
References for Hardness
Testing of Metal Materials |
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Additional Informations |
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Buderus hardness reference blocks are supplied with an official
calibration certificate (DKD) of the materials testing institute of Nordrhein-
Westfalen (MPA NRW).The distribution to the end consumers is
done only by the producers and distributors of hardness testing
machines and service centres.
The hardness determined on calibration, the hardness scale, a registration
number and the month and year of calibration are engraved
on each block.
The test surface of each block is supplied with a "B" as the manufacturers'mark
and additionally with a monitoring indentation marked
with a circle for Vickers,Knoop and Brinell blocks.On request a screen
on Brinell blocks (square/rectangular) and Rockwell blocks (square)
can also be applied..
The employees responsible at Buderus Edelstahl and at the
materials testing institute of Nordrhein-Westfalen will be pleased
to respond to any enquiries and provide additional information at
any time. |
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Special blocks, blocks with mill certificate and uncalibrated
blocks on request. |
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